1. Field of the Invention
The present invention relates to an image forming apparatus such as the electrophotographic copying machine and the electronic printer and, more particularly, it relates to an image forming apparatus provided with a developing unit for developing an electrostatic latent image on an image carrier with two-component developer consisting of toner and carrier.
2. Description of the Related Art
Conventionally, the image forming apparatus of this type is used in such a way that a developing unit which has been stored, previously filling it with developer consisting of toner and carrier mixed at a predetermined rate, is prepared and that it is set in the image forming apparatus. According to this system, however, toner becomes hardened during the storage of the developing unit. Or toner becomes deteriorated when developer is filled in the developing unit for a long time.
Recently, therefore, a developer is filled in the empty developing unit just before it is used. Some typical examples of this system are known. In a typical one, a top cover is removed from the developing unit after it is detached from the image forming apparatus, and two-component developer mixed at an appropriate rate, is filled from a bottle into the developing unit, and then the developing unit is set in the image forming apparatus. In another system, a developer-filled cartridge is set in a toner cartridge setting opening of the empty developing unit in the image forming apparatus and developer is filled from the toner cartridge into the empty developing unit in the same manner as toner is added to the unit under normal operation.
In the former system where the filling of developer is made by the bottle, however, developer must be filled in the developing unit after it is detached from the image forming apparatus and the top cap is removed from it. This filling operation is quite troublesome. In the latter system where the filling of developer is made in the same manner as the adding of toner, it takes too long to fill a large amount of developer into the developing unit, because the filling of toner allows a little and certain amount of toner to be added from the toner cartridge to the developing unit at a predetermined timing.